A number of designs are presently available which provide for distribution of pulverized fossil fuel, such as coal to the combustion zone of a furnace. In a great majority of these designs a fuel carrying conduit receives pulverized fuel from an external source and is connected to a burner for distributing the fuel to the burner. Both the conduit and the burner are relatively large in diameter and include a device for creating turbulence to enable the pulverized fuel to be distributed in a controlled manner so that it will burn more evenly in the combustion zone.
Since the coal fired burners described above are relatively large in diameter, a correspondingly large amount of primary air is required to deliver the fuel to the combustion zone which tends to create combustion limitations, especially under conditions calling for low furnace load.
Also, coal fired burners presently in use have a physical construction which is cumbersome and expensive to fabricate since their diameters can range from about one foot to over two feet, and are more or less fixed in position. Due to this size, adjustment is very limited and in most cases none is possible once the apparatus is installed in situ. Furthermore, repairs requiring removal of the burner are difficult to accomplish for the same reason.
On the other hand, gas and oil fired burners have relatively small fuel lines and atomizers, which are relatively easy to adjust both in regard to the positioning within openings in the boiler walls and with respect to fuel flow regulation under different load conditions. For example, gas and oil fired burners can be controlled so as to provide sufficient fuel for as low as about 20-25% full burner load rating, whereas coal fired burners have less flexibility and may only be decreased to about 40-50% of full load before the burner must be removed from service.